The present invention relates to a controller of an internal combustion engine.
There is an FFV (Flexible Fuel Vehicle) as a vehicle that can run on blended fuels of various compositions of gasoline and alcohol. With an FFV, an alcohol concentration in a blended fuel is detected by an alcohol concentration sensor, and operation parameters, such as a fuel injection amount of an engine, are controlled according to the detected alcohol concentration.
There is a related-art fuel property estimating device, with which, from an aspect of cost reduction, etc., an alcohol concentration sensor is not disposed, and the alcohol concentration is estimated from a detection value of an O2 sensor or other already-present sensor. For example, there is a related-art fuel property estimating device that estimates the alcohol concentration based on a feedback correction amount, determined from an exhaust air-fuel ratio detected by an O2 sensor, etc., only in a predetermined time in which predetermined enabling conditions are met (the conditions that fuel supplying has been performed and a cumulative fuel consumption amount after fuel supplying is no more than a fixed amount) (see JP-A-2004-251135 (Claim 1, FIG. 1, etc.)). This fuel property estimating device includes a plurality of concentration estimation enabling units, respectively corresponding to a plurality of disturbance factors influencing the exhaust air-fuel ratio, and is configured so that when a disturbance factor occurs, an enabling condition is not met at the corresponding concentration estimation enabling unit, corresponding to the disturbance factor that occurred, and estimation of concentration of a single component in a fuel is disabled. With this device, because the concentration estimation can be performed after the disturbance factor is eliminated, an estimated value can be improved in precision.
A purged fuel correction amount shall now be described. With a fuel controlling system of an engine, a purged fuel correction amount is set to compensate for an influence of purged vaporized fuel. A deviation of a feedback correction amount from a reference value during purging is deemed to be a contribution due to vaporized fuel and the purged fuel correction amount is determined based on this deviation. The purged fuel correction amount is reflected in feedback control only during purging. When the purge is cut, the purged fuel correction amount is decreased progressively in accordance with a degree of decrease in purging. In this case, if there is no change in fuel properties, because the feedback correction amount is a value (close to the reference value) from which the influence of the purged vaporized fuel is eliminated, the air-fuel ratio can be controlled with stability both during the vaporized fuel purge (that is, when the feedback correction amount and the purged fuel correction amount are used) and during the purge cut (that is, when just the feedback correction amount is used).
With an engine including a canister that stores vaporized fuel, the vaporized fuel is purged via a purge passage from the canister to an air intake system. The purged vaporized fuel contributes to combustion in a combustion chamber as a portion of the fuel and becomes a disturbance factor with respect to the correction amount of feedback control based on the exhaust air-fuel ratio. Thus, in a case where the alcohol concentration is estimated based on the feedback correction amount determined from the exhaust air-fuel ratio, even in a concentration estimation enabling period, in which concentration estimation enabling conditions are met, estimation of the alcohol concentration is disabled during the vaporized fuel purge. There is thus present in the concentration estimation enabling period, a concentration estimation executing period, in which estimation of the alcohol concentration is performed only when purging is cut and feedback control is operating.
On the other hand, during a period in which the vaporized fuel purge is performed, the estimation of the alcohol concentration is disabled and renewal of the estimated value is not performed because the period falls outside the concentration estimation executing period, the alcohol concentration may be changing greatly in actuality. In this case, when the vaporized fuel being purged is cut and the concentration estimation executing period is started, because renewal of the estimated value has not been performed at a point immediately after starting, feedback control is performed at a control amount (fuel injection amount) that is in accordance with the alcohol concentration estimated in a previous concentration estimation executing period. In this case, because the change of the alcohol concentration is reflected in the purged fuel correction amount but not reflected in the feedback correction amount, the alcohol concentration change amount (difference between the actual alcohol concentration and the alcohol concentration estimated in the previous concentration estimation executing period) is not reflected in the fuel injection amount immediately after the starting of the concentration estimation executing period accompanying the purge cut and an air-fuel ratio error occurs.
In particular, when the vaporized fuel purge is cut instantaneously, the air-fuel ratio changes rapidly in accompaniment. Although the changed air-fuel ratio must be converged quickly to a desired air-fuel ratio, the fuel injection amount for this can only be feedback corrected by a gain that is normally set for feedback control. It thus takes time to achieve convergence to the desired air-fuel ratio.